Expression of Apoptosis Gene Bok in the Rat Ovary

Lee, Yu Il; Shin, Hyun Woo; Lee, Jin; Kim, Mi young; Chun, Sang Young

Abstract

OBJECTIVE
Bok, Bcl-2-related ovarian killer, is a proapoptotic Bcl-2 family protein identified in the ovary based on its dimerization with the antiapoptotic protein Mcl-1. The present study examined the hormonal regulation and localization of Bok messenger RNA levels in the rat ovary during the follicle development.
METHODS
We used the female rats of SD strain. Bok mRNA levels in the ovary were determined by Northern blot analysis. In situ hybridization were performed to determine the specific ovarian cell type expressing Bok mRNA.
RESULTS
Northern blot analysis of ovaries obtained from immature rats revealed increasing levels of Bok mRNA during postnatal development. The major cell types expressing Bok mRNA were the granulosa cells of preantral and atretic follicles. Treatment of immature rats with diethylstilbestrol (DES) for 24-48 h increased ovarian Bok mRNA levels. Bok mRNA was remained the same levels in rats removed DES for 24- 48 h to induce apoptosis. High signals of Bok mRNA after DES treatment were detected in granulosa cells of early antral follicles. Treatment of immature rats with pregnant mare's serum gonadotropin (PMSG) for 12 h increased markedly ovarian Bok mRNA expression which was detected mainly in preantral and atretic follicles. Interestingly, low levels of Bok mRNA were also expressed in granulosa cells of preovulatory follicles. Treatment of PMSG-primed rats with human chorionic gonadotropin (hCG) stimulated strongly ovarian Bok mRNA expression at 6-9 h. At that time, Bok mRNA was expressed in granulosa cells of atretic and small growing follicles. In adult estrus cyclic ovaries, Bok gene expression was higher on proestrus and estrus than metaestrus and diestrus. Moreover, the highly increased expression of Bok mRNA was found in rat ovaries at 48 h after hypophysectomy.
CONCLUSION
These results demonstrate that Bok is one of proapoptotic Bcl-2 members expressed in early growing and atretic follicles during the ovarian follicular development. Gonadotropins induce a transient increase of Bok gene expression in granulosa cells of preantral and preovulatory follicles indicating some role in the ovulatory process.